This invention relates generally to the field of dentistry, and in particular to the reduction of teeth to facilitate placement of a dental prosthetic device, such as a crown. Or specifically, the invention is related to a dental tool and methods for measuring the amount of tooth reduction.
Artificial dental crowns are used as a restoration for teeth, and are particularly useful when teeth have been broken, have been weakened by decay, or have one or more large fillings. Dental crowns are constructed to fit over the remaining portion of the tooth to make the tooth stronger and provide the tooth with the shape and contour of the natural tooth. As such, crowns are often referred to as caps.
Dental crowns are typically fabricated outside the patient""s mouth and then installed in the mouth. The manner of installation may vary depending on the nature of the crown. For example, full crowns are employed to cover the entire surface of a tooth as well as the sides of the tooth. Partial crowns are inlays which cover the top surface and portions of the sides. Inlays are employed to cover central portions of the top surface and may also extend partially onto the sides. Finally, veneers are used to cover a side surface of a tooth. A detailed discussion of how such dental crowns may be placed onto a tooth is set forth in U.S. Pat. No. 5,525,059, the complete disclosure of which is herein incorporated by reference.
Dental crowns may be employed to treat a variety of conditions. For example, as previously mentioned, the tooth may have been previously weakened by decay or may have a very large filling. Another reason for using a crown is if the individual has discolored fillings and would like to improve the appearance of the tooth. As a further example, the patient may have had a root filling that needs the protection of a crown.
Dental crowns may be constructed of a variety of materials. For example, the crown may be constructed of a porcelain that is bonded to a precious metal. In such cases, the precious metal is used to form the base and the porcelain is applied in layers over the metal base. As another example, the crown may be constructed entirely of porcelain. Because these look very natural, they may often be used for the front teeth. Other examples include porcelain and composite resin materials, glass, and precious metals, such as gold and palladium. A further description of materials used for dental crowns and how they may be bonded to the underlying tooth is set forth in U.S. Pat. No. 6,183,256, the complete disclosure of which is herein incorporated by reference.
In order to receive a crown, the dentist must first alter the shape of the tooth to a size and shape most conducive for receiving a crown. To do so, the dentist will typically remove most of the outer surface of the tooth, leaving a strong inner core. Ideally, the amount of tooth removed will be about the same as the thickness of the crown to be fitted. After the tooth has been formed to the proper shape, an impression of the prepared tooth along with one of the opposite jaw is used to determine the manner in which the teeth are brought together when the patient takes a bite. The impressions are then used by a dental technician to fabricate the crown to the shape of the reduced tooth.
Determining the appropriate size and shape of the tooth to be fitted with a crown is a difficult process, especially when the tooth is near the back of the patient""s mouth. In such cases, it is nearly impossible to determine the amount of tooth that has been removed. However, determination of the amount of reduction is critical in order to ensure that the crown will properly fit. For example, if the tooth is reduced too much, the crown may be too loose. On the other hand, if not sufficiently reduced, the crown will be too large and will interfere with the patient""s bite.
In order to determine the amount of tooth reduction, some have proposed the use of a thin rubber strip upon which the patient is instructed to bite. If the dentist is unable to pull the rubber strip from the patient""s mouth, the dentist assumes that the tooth has not been sufficiently reduced in size. However, for teeth near the back of the patient""s mouth, it is nearly impossible to appropriately position such a rubber strip in the patient""s mouth.
Hence, this invention relates to a tooth reduction measuring tool along with methods for its use to facilitate proper tooth reduction when preparing for a crown.
In one embodiment, the invention provides a tooth reduction measuring tool that comprises a shaft having a proximal end and a distal end, with the proximal end defining a handle. A flexible loop extends from the distal end and has a thickness in the range from about 1 mm to about 2 mm. The loop defines an opening that is sufficiently large to be placed around a tooth. In this way, the loop may be positioned relative to a pair of opposing teeth, one of which has been reduced, such that the pair of opposing teeth are within the opening. After instructing the patient to bite down, the shaft may be pulled to move the loop into a gap between the opposing teeth to permit the dentist to evaluate the size of the gap based on the thickness of the loop. For example, if the dentist is unable to pull the loop through the gap, the dentist may determine that the tooth needs to be further reduced, at least on the back side of the tooth. Alternatively, the dentist may choose another measuring tool with a smaller sized loop and repeat the process to determine approximately how much more of the tooth needs to be reduced.
Optionally, the loop may include a marking material that produces a mark when engaging the tooth. In this way, when the dentist pulls on the loop and it engages the tooth, a mark will be produced on a loop or the tooth. The dentist may then evaluate the position of the mark to determine the location where additional tooth reduction needs to occur.
In another aspect, the loop may be constructed of a polymer so that the tool may be constructed in a relatively inexpensive manner. Further, the shaft may also be constructed of a polymer and integrally formed with the loop. In this way, the measuring tool may be disposed of after use. Further, the measuring tool may be placed into a sterile package so that the measuring tool will remain sterile until use.
To place a crown on a tooth, an initial amount of material is removed from the target tooth. The amount of removed material is then measured using the measuring tool by grasping the handle and placing the loop around or adjacent to the target tooth. The patient is then instructed to bite down to move an opposing tooth generally adjacent to the target tooth. The handle may then been retracted to pull the loop into a gap between the target tooth and the opposing tooth. The size of the gap may then be evaluated based on the thickness of the tooth relative to the gap as previously described. If needed, additional material may be removed from the target tooth or the opposing tooth if the loop is unable to move through the gap. Once the target tooth is appropriately sized and shaped, an impression may be taken and a crown formed. Following formation of the crown, it may be bonded to the target tooth.
In some cases, the loop may extend from the shaft at an acute angle to facilitate manipulation of the loop when measuring the back teeth. Alternatively, the loop may extend axially from the handle.